Desymmetrization of Cyclopropenes
Final Report Abstract
A highly enantioselective palladium-catalyzed carbozincation of cyclopropenes has been developed and the intermediate cyclopropyl zinc species were successfully trapped with a range of electrophiles. For the capture with carbon electrophiles, a transmetalation to copper was found to be necessary. This one-pot procedure furnished functionalizied cyclopropanes with an excellent diastereoselectivity and enantioselectivity. Different symmetrically substituted cyclopropenes have been studied. In addition, investigations towards the use of different dialkylzinc reagents and suitable procedures for the preparation of non-commercially available zinc reagents were carried out. However, the best results were obtained using cyclopropene 4 and diethylzinc. The areas alluded as well as the facial selectivity using asymmetrically substituted cyclopropenes still remain to be further investigated. Focus has also been paid to the development of a nickel-catalyzed carbozincation. The influence of solvent, nickel source and ligand has been studied but the reaction was still plagued by low yields due to formation of undesired byproducts.
